Mobile network operators (hereinafter “operators”) may subsidize the purchase prices of end-user mobile devices (e.g., mobile phones) to boost subscription to their services. To ensure that mobile devices purchased at the subsidy prices are indeed used on the network of the operator providing the subsidies, the operator may place an operator lock on such devices. Hereinafter the operator subsidizing the device purchase and instituting the operator lock may be referred to as the home operator, and the device with the operator lock the locked device.
Ideally, an operator lock works by blocking the mobile network functions of the locked device when the universal integrated circuit card (UICC) (also colloquially referred to as the SIM “Subscriber Identity Module” card) (either removable or embedded) installed in the locked device does not come from the home operator. In practice, the conventional operator lock is based on the IMSI (International Mobile Subscriber Identity) information stored on the UICC, which uniquely identifies the user subscription.
Each operator is associated with a 3-digit Mobile Country Code (MCC), which identifies the country the operator is located in, and a 2 or 3-digit Mobile Network Code (MNC), which identifies the operator within the country specified by the MCC. The first three digits of an IMSI is the MCC, and the next two or three digits is the MNC. In other words, the combination of MCC-MNC, which corresponds to a specific operator, can be derived from an IMSI. Conventionally, an operator lock determines whether the MCC-MNC combination derived from the IMSI matches the MCC-MNC combination of the home operator, and 1) permits the mobile network functions when there is a match, or 2) blocks the mobile network functions when there is not a match.
The conventional operator lock has worked well until the advent of multi-IMSI roaming. Multi-IMSI roaming allows user to access more preferential roaming rates with roaming partner operators with whom the home operator has roaming agreements. With multi-IMSI roaming, a roaming partner operator's IMSI, which is pre-stored or remotely provisioned on the UICC, becomes active when the user device leaves the home operator's coverage area, and roams onto and registers with the roaming partner operator's network.
Therefore, to ensure the proper functioning of multi-IMSI roaming in light of the multiple IMSIs that may be used throughout the home operator's network and the one or more roaming partner operators' networks, a conventional operator lock needs to be adapted to accommodate not only the home operator's MCC-MNC combination, but also the roaming partner operators' MCC-MNC combinations.
Consequently, a loophole is created. Because the IMSI-based operator lock accommodates the roaming partner operator's MCC-MNC combination and is based on the active IMSI, the locked device will have full functionality when a roaming partner operator-issued UICC is installed in the locked device. This is inconsistent with the desired behavior of the operator lock, and may negatively affect the home operator's revenue if a significant number of mobile devices purchased from the home operator at subsidy prices are used not with home operator-issued UICCs, but with roaming partner operators-issued UICCs instead.